(1) Field of the Invention
The invention relates to a liquid crystal television adjustment system, a liquid crystal display unit adjustment system, and a liquid crystal display unit, capable of implementing white balance adjustment.
(2) Description of the Related Art
For color reproduction in a display unit, it is necessary to cause a color signal of a picture signal to sufficiently correspond to a color to be displayed in the display unit. In particular, it is a white color, as an achromatic color, that is indispensable for color display, and it should never happen that a change occurs to the chromaticity point of the white color due to a change in gradation of the achromatic color. In this connection, since an input-to-luminance characteristic is relatively well aligned among R, G, B in a cathode-ray tube display unit, it is possible to reproduce a white color constant in chromaticity against identical R, G, B input levels by aligning respective cut-off points for R, G, B in a cathode-ray tube with a black level of the picture signal, and by fixing an amplitude ratio among R, G, B on the basis of an amp gain.
However, with a liquid crystal display unit, the input-luminance characteristic thereof differs from that of the cathode-ray tube display unit, and further, an amplitude ratio among R, G, B is not constant, so that chromaticity of the white color undergoes a change according to a change in a gradation level of the achromatic color, thereby causing a problem in that accurate color reproduction cannot be implemented.
In JP No. 2001-238227-A, there has been disclosed a liquid crystal display unit capable of adjusting white balance with the use of a look-up table prepared beforehand so as to be able to obtain white balance, including a V-T characteristic of a liquid crystal panel.
In JP No. 1999-317417-A/, there has been disclosed a white balance circuit comprising a feedback circuit capable of adjusting a gain control signal level if an output level of a picture signal exceeds a reference voltage.
In JP No. 2002-305734-A/, there has been disclosed a liquid crystal display unit wherein an average picture level (ALP) is detected from RGB signals by an average picture level (ALP) detection circuit, and a black level is lowered by deceasing a gain with chromaticity of a white color being kept constant when the ALP is high while lowering of the black level is checked by increasing the gain regardless of an RGB ratio when the ALP is low.
With a conventional display unit of a type that does not employ natural light, such as that of a liquid crystal television, as respective outputs of RGB colors are increased, color saturation is reached at a point in time when an open-area ratio of each of liquid crystal cells for the respective colors is turned to a 100%, so that it has been impossible to implement adjustment itself even if the outputs are further increased. In addition, having taken into consideration chromaticity variation in a backlight lamp, variation in open-area ratio among liquid crystal cells, and so forth, there has been the need for making adjustment of the white balance on the extremely inner side of a dynamic range. More specifically, in the case of adjusting the white balance by use of the two-point tracking method, it has been necessary to secure an adjustment margin for open-area ratios of the respective liquid crystal cells (higher luminance side: 70 to 100%, lower luminance side: 40 to 0%) such as the open-area ratios of the respective liquid crystal cells starting the adjustment of the white balance on the higher luminance side, set to 70%, and the open-area ratios of the respective liquid crystal cells starting the adjustment of the white balance on the lower luminance side, set to 40%, so that it has been impossible to achieve precision in adjusting the white balance.